1. Field of the Invention
This invention relates to a method and apparatus for modelling a system which includes the transmission and reception of signals and is particularly useful for modelling radio communications systems and radar systems.
2. Description of the Prior Art
Designers of communication systems face a very complex task not only because of the large number of factors or variables involved in the design, but also because performance objectives and cost requirements may conflict. Frequently the designer is faced with an enormous span of possibilities. For example, for a cellular radio network, base station positions must be chosen and other factors such as antenna location, antenna power, antenna direction and frequency allocation chosen. Installation of the infrastructure and equipment for the communications network is typically a very costly and time consuming operation. This places great reliance on the success of the design.
Systems which make use of radar are also subject to the same design problems. Typically the radar sensor designer wishes to propose a configuration which will meet the performance objectives with the minimum cost. The equipment required is typically very expensive to manufacture and install and there is a large number of options involved. For example, choice of configuration (e.g. single beam, multi-beam, mechanical scan, electronic scan, etc.), choice of waveform modulation (e.g. narrowband, wideband, pulsed etc.), choice of operating frequency (e.g. high frequency through centimetric to millimetric) and choice of signal processing method and technology.
To date, communications systems modelling and radar systems modelling has been largely confined to models which have explored variants upon one basic configuration in support of particular system developments (e.g. a model of a specific communications system). Current methods for implementing such models usually satisfy the requirements of the project for which they were created. However, these models typically also suffer a number of significant drawbacks such as:
making little or no re-use of preceding communication system models or parts of these PA0 incompatibility with other communication systems models PA0 the need to test the entire communication system model from scratch PA0 these models are typically difficult to understand and maintain PA0 these models are difficult to modify and hence often have only a short lifetime PA0 the models are often difficult to use by anyone other than the creator. PA0 (i) creating a number of blocks, each block comprising a piece of program code and each block being a representation of an aspect of the system, wherein each block has a pre-defined output; and PA0 (ii) forming connections between the blocks, each connection comprising a bus for transferring data between blocks, wherein each bus has the same pre-defined format such that in use blocks can be connected in different configurations without redefining the block outputs. PA0 (i) a memory arranged to store a number of blocks, each block comprising a piece of program code and each block being a representation of an aspect of the system, wherein each block has a pre-defined output; PA0 (ii) connections between the blocks, each connection comprising a bus for transferring data between blocks, wherein each bus has the same pre-defined format such that in use blocks can be connected in different configurations without redefining the block outputs. PA0 (i) representing the signal using a combination of pre-specified waveform types; PA0 (ii) transferring the representation of the signal between blocks using one or more of said buses; and PA0 (iii) regenerating the signal from the representation. This provides the advantage that execution times for the simulations created using the model are reduced. At the same time the accuracy of the simulations is not significantly affected. Parts of the model which it is not required to analyse in detail can be modelled using the compact signal representation to speed up processing. However, other parts of the model can easily be investigated more specifically by using a full, sampled form for the signals. This gives the advantage that both types of modelling can be used at the same time in the same model. Different parts of the model can be examined in detail simply by rearranging the blocks, including the analyser and regenerator blocks in the simulation environment. PA0 (i) representing the signal using a combination of pre-specified waveform types, said waveforms comprising one or more of: a pulse, a sinusoid, a constant, and a distribution. This provides the advantage that a compact representation of the signal can be simply and effectively provided by using only four component waveform types.
A particular problem when modelling mobile telephone communications systems and radar systems is that relationships between components of the system are continually changing and this is difficult and complex to model. For example, in a mobile telephone system, a significant number of mobile telephone subscribers are moving about at any one time. The physical location of the terminals changes. Similarly, in radar systems, the location of a transmit antenna on a ship typically moves and the location of targets, such as aircraft, also move. Any model of these types of systems needs to be able to take into account the movement of components such as terminals and determine how this will affect factors such as the transmission of signals within the system. For example, as a mobile phone user moves into the "shadow" of a building, signals may become harder to receive.
A further problem that occurs when it is required to model systems which include the transmission and reception of a signal is that execution times for the simulations can be very long. This is because, in order to describe fully the signal a large number of samples (above the Nyquist limit) need to be taken from the signal. This large number of samples must then be processed through the various stages of the model which is time consuming, especially when complex calculations are involved. If fewer samples are taken in order to reduce the simulation time there is a reduction in the accuracy of the results.
It is accordingly an object of the present invention to provide a method and apparatus for modelling a system which includes the transmission and reception of signals which overcomes or at least mitigates one or all of the problems noted above.